For watch collectors, Patek Philippe is a name that is synonymous with perpetual calendar chronographs. They were the trailblazers of serial production of the complication and created the first serially produced model when they introduced the 1518 in 1941. The follow-up, ref. 2499, was released just ten years later in 1951. Each reference was made in small amounts, with only 281 examples of the 1518 and 349 of the 2499. As a consequence, they are among the most coveted vintage watches ever made. But Patek didn’t stop there. In 1986, they introduced the 3970, the first perpetual calendar chronograph that they truly produced at scale. From 1986 to 2004, roughly 4,000 examples of ref. 3970 were produced, the first series of which was the immediate successor to the 2499. The second series was the first to feature a screw down caseback for increased water resistance.